I got some pretty yarn that goes from thick to thin and back again with various colors. I tried knitting it just garter stitch on large needles to make a scarf but it did not look good. I tried a few other things but have not figured out what to do with it. Here is the yarn:
what can I do to knit it and make it look as pretty as it is?
I wanted to make a scarf or something.

What a koinkidink! After reading and replying to your post, I also started a project using thick/thin yarn. Yours looks bulkier than mine, however.
Here's a sample of what I'm doing, using size 9 needles and the bramble stitch (easy). I remember from previous projects that small samples using this type of yarn just look sloppy, so it wouldn't be suitable for doll clothes, but when you get a large piece worked up, it all falls into place.

With regular yarn, each of these "bumps" would look the same. On a large piece it would even out. Here, it just looks like sloppy knitting.